$464,171.83
The discount rate is used to calculate the present value of an asset you expect to get in the future. The formula is
PV = FV/(1+R)^n
where
PV = Present Value
FV = Future Value
R = Rate
n = Number of periods
So let's look at the return for the first 3 years
Year 1
PV = $120,000/1.12 = $107,142.86
Year 2
PV = $180,000/1.12^2 = $180,000/1.2544 = $143,494.90
Year 3
PV = $300,000/1.12^3 = $300,000/1.404928 = $213,534.07
So the current value is
PV = $107,142.86 + $143,494.90 + $213,534.07 = $464,171.83